Measuring instrument



Dec. 26, 1939. c. B. MOORE Er AL MEASURING INSTRUMENT Filed Feb. l0, 1938 5 Sheets-Sheet l INVENTOR.

o OM W M.J N BC. R NT m Asll T MU A EG Dec. 26, 1939. c. B. MOORE l-:r AL

MEASURING INSTRUMENT Filed Feb. l0, 1958 5 Sheets-Sheet 2 INVENToR.

UGUST C. JAUSS ATTORNEY FIGZ.

COLEMAN B. MOORE 71W @MA Y 26, 1939. Q B MOORE ET AL y 2,184,430

MEASURING INSTRUMENT Filed Feb. l0, 1958 5 Sheets-Sheet 5 FIGB IIIIIIIII l ll l III IN V EN TOR.

COLEMAN B. MOORE AUGUST C. JAUSS 'BY ATTORNEY Dec. 26, 1939. c B. MOORE ET'AL MEASURING INSTRUMENT Filed Feb. lO, 1938 5 Sheets--Sheei'l 4 INVENToR.

B. MOORE c. JAUSS ATTORNEY E.

c. B. M'ooRE ITAL. y2,184,430 mmsuRING INSTRUMENT Dec. 26, 1939.

Filed Feb. 1o, 195s 5 sheets-sheet 5 INVENTOR. COLEMAN B. MOORE AUGUST C. JAUSS BYR'W A T TORNEY Patented Dec. 26, 1939 UNITED `S'IAI'ES PATENT OFFICE' MEASURING INSTRUMENT Coleman B. Moore, Carroll Park, and August. C.

Jauss, Aidan, Pa., assignors to The Brown Instrument Company, Philadelphia, Pa., a corporation of Pennsylvania Application February 10, 1938, Serial No. 189,804 I 17 Claims.

Our present invention relates to measuring instruments, and particularly to measuring instruments of the self-balancing potentiometric type which maybe used to adjust a member according to the varying values of a measurable potential difference, such as the voltage of a thermocouple responsive to a variable temperature.

The general object of our invention is to provide an instrument of the above-mentioned type, which is reliable and accurate in operation and which includesmeans to adjust a potentiometer slide-wire in a direction and .amount in proportion to the deviation of a galvanometer 16 pointer, the coil of which may be in circuit with a thermocouple.

The improvements in the present f invention standing of the invention, however, its advantages and specific objects obtained with its'use, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and described a preferred embodiment of the invention.

Of the drawings: Fig. l is a front' view of a potentiometer slidewire adjusting mechanism;

Fig. 2 is a view similar to Eig. llwith the front plate and slide-wire removed for the'sake of clearness;

tials Fig. 4n is a front viewofa modicationwith certain parts omitted for the sake ofv clearness;-

Figs. 5 and 6 are further vfront views of other modifications with parts' omitted for thesake of 'clearness In the' mpdincation of Figs. pagina positionof a moving velement such as a galvanoineter'pointer is periodically, measured by a feeler which in 5o turn positions a secondary feeler in accordance with the position of the pointer. The position of the secondary feeler controls the application of a brake `to the normally rotating parts of either one Aof a pair of differentials While the normally stationary part of each differential is geared to This provides for' Fig'. 3 isy a section through one ofthedifferenl a potentiometer slide-wire contact. The differentials are driven in opposite directions sok that the slide-wire contact will be driven thereby in one direction or the other depending upon the position of the galvanometer pointer and the secondary feeler when a brake is applied to a normally rotating part thereof. The distance of the pointer from its mid-position is also used to control the amount of movement of the slidewire contact by varying the time that the brake is applied to the differential.

Potentiometric circuits .of the type contemplated herein are well known, such, for example,

as disclosed in the Harrison Patent 1,898,124, andiv include a known source of voltage impressed --across a resistor, commonly termed the instru.-

ment slide-wire, the galvanometer and source of variable voltage being connected in series to oppose the known voltage across a variable portion of said resistor. When the variable voltage,` for a given adjustment of the slide-Wire, is equal and opposite to the knownvoltage, the galvanometer is in its null position, but on an increaseabove or decrease below the known voltage of the` unknown voltage, the galvanometer will be deected in one direction or the other respectively proportionately to the magnitude of the increase or decrease. This invention is concernedY with the means by which deflections of said galvanometer control slide-wire adjustments to continuously rebalance the potentiometer system.

Mounted upon standard I are the two supporting plates 2, 2a, for the mechanism to be described. Journaled in the plates 2, 2a is a shaft 3 which extends through plates 2. and 2a and isjournaled therein. Attached to the front of thisshaft is a member 6 upon the upper end of which is adjustably mounted a slide-wire contactor. 1.- Adjustably fastened to the member 6 byscrew 8 is a lever 9 having a counter-weight Il on its lower end in orders to balance the contact 1 as it rotates with the shaft 3 in a manner Yto be. described. Attached to the front of plate 2 o o-axial with shaft 3, is potentiometer. slidewire support 4 upon the surface of which is mounted a slide-wire'. 5. As the shaft 3 rotates,

itlwill move contact 1 around the surface of the slide-wire and thereby adjust thelsetting of the galvanometer.

Fastened to the back supporting plate 2a is a galvanometer i2 whichl is used to record -small 'currents coming fromany desired type of primary element, such as a thermocouple. As'small currents flow through the coil of the galvanometer, the pointer I3 is deflected to one side or the measure the position of pointer i secondary feeler 36 that is pivoted at 31. ,Moveother of the neutral point where it is then clamped between stationary member I4 and movable member I5 which` is biased toward I4 by springs I6. The means for moving member I5 downwardly to free the pointer consists of a link I1 (see Fig. 2) fastened at its upper end to member I5 and at its lower end to one arm of a bell-crank I8 pivoted on shaft I9 and having on its other arm a roller 2I which is acted upon by a cam 22, which along with a cam 23 and a gear 24 is mounted for rotation on shaft 3. The gear 24 and the two cams are driven through a' train of gearing from a motor 25, fastened between plates 2 and 2a.

Also pivoted on shaft I9 is a lever 21 having on its lower end a roller 26 bearing against cam 23 under the bias of spring 33. The upper end of lever 21 carries a roller 28, which at times acts on a cam edge of member 29 to force that member to the left around its pivot 3| to which it is attached. A feeler 30 adapted to engage and I3 is also attached to pivot shaft 3| and is biased, along with lever 29, in a counter-clockwise direction-by spring 32. The arrangement of cams 22 and 23 is such that in their rotation, the low portion of cam 22 will come under roller 2I and thereby permit bellcrank I8 to turn under the pull of springs I6 on member I5 toclamp the pointer I3 in position just prior to the time the lowportion of cam 23 comes under roller 26. When this occurs, lever 21 is moved clockwise under the bias of spring 33,'anvd the feeler 38 and lever 29 are moved counterclockwise under the bias of spring 32 until feeler 30 engages the end of pointer I3, which is now clamped in position.

Continued rotation of cams 22 and 23 will move feeler 30 away from pointer I3 beforeithe pointer is unclamped.

As the feeler 30 moves into engagement with pointer I3, a. secondary feeler will be positioned in accordancel therewith. lTo this end, the lower end of lever 29 is provided with a slot in whichis adjustably positioned a pin 34. Each side of this pin is embraced by a finger 35 or 35a of a ment of pin 34 on lever 29 will accordingly move the secondary 'feeler and a pin 38` on the lower end thereof a corresponding amount. Inasmuch as the feeler 30 is to be moved to its inactive position during the ensuing operations, the finger 35a is separate from nger 35 and secondary feeler 36 and is biased toward finger 35 by spring 35h. In this manner the secondary'feeler can be l retained in its position while feeler 38 is moved,

since finger 35a -will give with respect to finger 35.-

The nger 35a mainly serves the purpose of pre-` venting over-travel of secondary feeler 36.

The position of pin 38 is used to determine the v@(rrelative positions .of a pair of feeler cams 39 and 39a that in turn determine the length of time that'a brake is applied to the normally rotating member of a differential. Each cam 39 and 39a is provided with an inturned edge 42 .or 42a and is pivoted to move 'around shaft 4I or '4I a,

respectively. y

The above-mentioned differentials are of the planetary type and are mounted, one on. each shaft 45 and 45a. Sinceea'chl differential andl the'parts relating thereto are identical, only one will be described, corresponding parts of the other being designated with the same reference character and the suffix` a.

As shown more clearly in Fig. 2, the shaft 45 has thereon a gear 44 which is in mesh with differentials and their actuating levers.

and driven by gear 44a on shaft 45a, which gear is in turn driven by a constantly rotating pinion 43 on the shaft of motor 25. The effect is that shafts 45 and 45a are driven in opposite directions to drive the differentials in opposite directions.

From Fig. 3 it will be seen that each differential consists' of a pinion 46 on shaft 45 meshing with pinion 41, fastened to gear 48 which is rotatable around shaft 45. Also mounted for rotation on shaft 45 is an internal gear 49 having a smooth outer surface and having its teeth in mesh with pinion 41. It will be seen that since pinion 46 is constantly rotated, the power will tend to split two ways, to rotate gear 48 or to rotate gear 49 and will take the course of least resistance, asl

is true with all differentials. On the outer end of shaft 45 is a cam.5I having a roller 52 on the front thereof, and, in addition, the shaft 45a has in front of cam 5Ia a gear 53. The gear 53 drives an idler 5'4 which in turn drives gear 24 to which cams 22 and 23 are attached as above ymounted between the plates 2 and 2a in a suitable manner and serves to locate stud shafts 55, 55a upon which are mounted brakes for the The following parts are also duplicated on each side of the instrument, so they will only be described in detail with respectto one side. Rigidly fastened to shaft 55, back of plate 2b, is a member 58 whose end below and to the left of the shaft 55 is bent downwardly as shown. The upper end of this member 58 is formed as a stop 59 for pin 68 on gbear 61, while between the shaft 55 and the lower end is a projection 64 that is adapted to bear on the outer surface of internal gear 49 of' the differential and act as a brake therefor. A journal 6l is provided at the bend of this member 58 that loosely surrounds shaft 4I, andV pivoted on journal 6I is a cam follower 62 that has on one end a roller adapted to bearon the surface of cam 5Il and on the other end an en-v largement through which is threaded an adjusting screw 63 which at times bears uponedge 42 of feeler cam. 39 to move that cam counterclockwise. 'The -front of shaft 55 has rigidly attached to it a bell-crank 56, the outer end of whichis joined to the-outer end of feeler cam.

39 by a spring 51, and theinner 'end of which has an. arcuate portion that is acted uponl by4 roller 52 on the front of cam 5I during its rotation. This lever at times serves to positively lift brake 64 from internal gear 49 of the differential-. A link 65 having a slot 65a in one'end is connected to the lower end of member 58a while the lower end of member 58 has a pin 66 extending into the slot to form a lost motion con- Y a newsetting of the feelers 36 and 36 has place to start a new cycle.

29 so that feeler 39 can move under the bias of spring 32, into engagement with the pointer I3 to measure its position and thereby move secondary feeler 36 and pin 38 to a position dictated by the position of the pointer.

During the above operation cams 5I and 5Ia have been rotating counter-clockwise and clockwise respectively, and just as pin 38 is properly positioned, the low portions of these cams start to come under the lrollers on levers 62 and 62a -respectively, to lower the levers around journals 6I and through the adjusting screws 63, 63a permit the feeler cams 39 and 39a to be lowered toward pin 38. If this pin is not in its m'dposition, one of the feeler cams will contact it before the other. If, for example, feeler cam 39 contacts pin 38v rst, its downward movement will be arrested and edge 42 will become a xed point. then permit the roller on follower 62 to 1ower, with screw 63 on edge 42 as a fulcrum. This is possible since journal 6I around which follower 62 rotates is larger than shaft 4I. As the follower 62 is lowered, the journal 6I, part of lever 58, is also lowered under its counter-clockwise gravitational bias on shaft 55 until brake-member 64 engages the-surface of the internal gear 49 to apply a braking force thereto. yWhen the brake 64 engages the surface of internal gear 49, the line of least resistance for the differential is to cause pinion 41 to walk around the inside of gear 49 and thus rotate gear 48 and gear 61 on shaft 3 to rotate that shaft andthe slide-wide contact 1. As lever 58 carrying journal -6I moves in a counter-clockwise direction to apply the brake 64 to gear 49, the pin 66 on the lower end of the lever is moved to the right end of slot 65a. I

While the above-described operation is occurring, the feeler cam 39a is moving toward pin 38. When feeler cam 39a engages pin 38 the above operation takes place through its corresponding lever system, except that when the member 58a moves clockwise under its gravitational bias to. apply brake 64a to internal gear 49a, the right end of slot 65a will move pin 66 to the left thus removing brake 84 from gear 49a. The action of springs 51 and 51a balance each other,` and as neither brake 64 is bearing shaft 3 and the contact 1 will be driven for a period of time equal to that which it takes feeler cam 39a to contact pin 38 after feeler cam 39 has 'contacted it.

In order to prevent rotation .of shaft 3 during the rising of feeler cams 39 to their initial positions, the rollers 52 will comefu'nder the arcuate portions of bellcrank levers 65 just as thehigh portions of the cams 5I are starting under followers 62 to raise the-feeler cams 39 and free pin 38. As rollers 52 come under the arcuate portions of the bell-cranks 65 they force the bell-cranks, shafts 55 to which` they are attached, and members 58 which are also fastened to shafts 55 to move counter-clockwise (member 58a) and clockwise (member 58) for an extent limited by pin 66 and slot 65a to hold brakemembers 64 out of engagement with gears`49. By the time that 'feeler cams 39 and 39a have reached the top of their strokes and, start down, taken If feeler cam 39a strikes pin 38 flrstg'bthe reverse of the above operation is .true and-projec- Continued rotation of cam 5| will.

tion 64a will brake internal gear 49a. If bothi feeler vcams 39, 39a contact pin 38 at the same time, indicating a neutral position of the galvanometer pointer, neither of the brakes 64 or 64a will be applied to their respective gears yand the slide-wire contact will not be rotated.

The modification disclosed in Fig. 4 performs its slide-wire adjusting operations by braking.

the normally moving member of either one of two oppositely driven differentials as wasdone in Fig. l, but differs therefrom in the manner of setting the feelers from the position of the galvanometer pointer and in the manner in which the brake is applied to the differentials. In this modification there is also provided a' means for giving a continuous correcting movement to the slide-wire 4 against finger 35 on secondary feeler 36 to'properly position that member in accordance with the position of the pointer.` A brake 8l in the form of a bell-crank is provided to hold the secondary feeler 36 in place during the remainder of the operating cycle, and does so by engaging a brake edge 36h thereon. This brake is applied by spring 82 and releasedby engagement between a roller and a cam 19 that is mounted on a shaft 1I along with and in timed relation to cam 23 that controls feeler 30. f v

Movement of secondary feeler 36 is transmitted to an actuating member 16 by means of a pin 36a on itslower end acting against the sides of a slot 11a in an arm 11 that is rigidly attached to member 16. The actuating member 16 is supported by and pivots around a pin 18 on the horizontally extending arm of a bell-crank 14 that is in turn mounted for pivoted movement around point 15. Movement is imparted to the bell-crank 14 and actuating member 'I6 in a counter-clockwise direction by a spring 92 and in a clockwise direction against the force of this spring by a cam 13 that is also mounted on shaft 1I in timed relation lto the other cams thereon. A brake-member for the differentials is pivoted on the frame of the device at 84 and end, that overlie inclined edges 16a of the actuating member 16. Above the pivot 84 of the brake-member is an edge 81 that isadapted to engage the surface of either internal gear 49 of the differentials. A means 89 for holding the edge'81 in continuous engagement with one of the gears 49 or 49a in the event of an excessive galvanometer deflection is also pivoted at 84 back of the brake-member. The upper end cf member 89 is normally held in place by'a leafl spring 88 on the brake-member against the toggle action of a spring 92 that has its lower end fastened to a stationary part of the device. This member 89 has two forwardly bent edges 98 that are parallel to and outside of edges 86, and has two pins 9| that are adapted toengage against the sides ofthe brake-member 85 to force its edge 81 against one of tl'iegears 49 of the differentials.

When the above-described positioning operations of feeler 30 and secondary feeler 36 take place, the high portion of cam 13 is under roller 14a and member 16 is positioned downwardly from the position shown, so that, as it is moved to one side or the other according tothe position of the pointer, the edges 16a will not strike the edges 86. As cam 13 rotates to bring its low portion under roller 14a, spring 92 will rotate the bell-crank 14 counter-,clockwise around pivot 15 to move actuating member 16 upwardly. Ii' the pointer was in its mid-position the parts will assume the position shown and on its upwardV movement neither edge 16a will engage its corresponding edge 86. If, however, the pointer I3 is to one side of its mid-position, member 16 will be moved out of the vertical an amount depending upon this deviation, and on its upward movement an edge 16a will engage an edge 86 to tilt the brake-member 85 around 84 and move edge 81 into engagement with one of the internal gears 49 or 49a. As on of gears 49 or 49a is stopped rotating, the corresponding gear 48 or 48a will be rotated to rotate gear 61 and drive the slide-wire. The direction of rotation of the slide-wire will therefore depend upon the direction of deviation of the pointer I3 and the length of time it is rotated will depend upon the length of time an edge 16a is in engagement with an edge,86. Since cam 13 is rotating at a constant speed, this time will vary with the amount of deflection of pointer I3 because the more member 16 is moved out of the vertical, the sooner oneA vof its sloping edges 16a will engage the corresponding edge 86.

If the galvanometer pointer should deflect an excessive `amount to either side, the actuating member 16 will be moved by pin 36a aroundits pivot 18 to such an extent that the inner end of one of the edges 16a will be beyond an edge 86 and will underlie an edge 90. Upon the subsequent upward movement of member'16 by bellcrank 14, edge 98 will be engaged to move the upper end of member 89 out from under spring 88 and yspring 92 will then toggle this member over until a pin 9| engagesthe side of brakemember 85 to bring edge 81 against the surface of one of gears 49 or'49a. The braking of gear 49 or 49a will cause, through its differential, a continuous movement of slide-wire contact 1 until the following cycle or until the deflection of pointer I3 causes movement of the member 16 to a position where the member 89 toggles into neutral position with its upper end under spring I' 88, thereby relieving the brake.

The modification shown in Fig. is similar to that disclosed in Fig. 4, but differs therefrom in lthe manner of setting the lever 36 and in the manner of applying the brake to the internal gears 49 and 49a of the diierentials. In this modication the feeler 36 is pivoted around the pin 31 upon which the secondary feeler 36 is also pivoted, and the pin 34` is -adjustably mounted in a slot near the lower end of the feeler.

An actuatingV member 96 having surfaces 96a and' 96b which engage the edges 86 or 90 depending upon the amount of deflection of the pointer is pivoted at 36a on thelower end of secondary feeler 36. Also pivoted about an axis that is coaxial with and behind point 36a, when 36ais in its neutral position, are two curved actuating levers 91, 91a having on one, end rollers 98, 98a and having the other ends.99, 99a curved backwardly as shown so that the edges IIII, IIHa thereon can contact the lower edge of member biased towards each other by a spring |02, and the rollers 98 and 98a are therefore held in contact with cams 93 and 93a respectively, which cams are mounted on shaft 94 that is connected by gearing (not shown) with shaft 1I and shafts 45 and 45a of the differentials. All of these shafts are driven in the proper timed' relation by a motor similar to motor 25 of Fig. 1.

In its operation, this modication has the feeler 36 moved up against p ointer I3 to adjust lever 36 and has brake 8| applied to edge 36b` in a manner identical to that described in detail in connection with Fig. 4. As-lever 36 is adjusted the actuating member 96 is moved tof; the right or the left, depending upon the position of the pointer I3. The parts are shown in the drawings in the position. just after the setting has been compleetd for a neutral position of the galvanometer. Continued rotation of shaft 1l will leave the low portions of cam 19 under roller 80 and will bring the high portion of cam 22 under roller 26 to m'ove feeler 30 to itsinactive position forthe rest of the cycle. Finger 35a will give with respect to nger 35 under the tension of spring 31 to permit this to occur. Due to the gearing between shafts 1I vand 94, the low portions of cams 93 and 93a will start to come under rollers 98, 96a so that spring |02 can `pull the lower ends of levers 91, 91a toward each other just after the high portion of cam 22 comes under roller 26. In the setting shown, that is midposition, edges IDI, IIlIa will engage the lower edge of member 96 simultaneously so that there will be no tiltingof 96 and no contact between either edge 96a and either cdge 86, and, therefore, member 85 will not be tilted so that there will be no braking action on either of the internal gears 49 or 49a.

If, however, member 96 has been adjusted, say to the left, edge IIII will strike the lower edge of 96 and force the left-hand edge 96a into contact with the left-hand part 36 to tilt brakemember 85 in a clockwise-direction around its pivot 84 and apply the brake-member. 81 to the surface of internal gea 49. This, because of the dierential construction described above, will cause gear 48 to rotate gear 61 and the slidewire. If member 69 had been moved to the right, in a like manner the brake would have been applied to gear 49a. The braking action continues Vuntil edge IIlIa comes into contact withv the other side of member 96 and moves that member back into a level position to stop the braking action. The

tacted by either edge IUI or edge IllIa, the upperI end: o1' member 89 is moved out from' under spring 88 and member 89 is toggled over by the action of spring 92, and one or the other'of pins 9I will contact brake-member 85 to lock it in position. This condition will -exist continuously through thecycles until the galvanometer deiiection bring members 36 and 96 back to a position where member 89 toggles into, neutral position and is held by spring 88, thus relieving the brake. By differentially operating the brake through member 96, the effect of wear is veliminated since both sides of 96 and both edges IUI, Il lIa are worn approximately an equal amount.,

The modincanon- 0r-Fi. s istne same-as that ing pin |03 on its upper end.` This pin |03 extends through a slotV |04 formed in the lower end of one arm of a bell-crank .|05 that is mounted to move around shaft 3, to the rear of the slide-wire support 4. A wide-faced pinion |01 is mounted on the end .of the horizontal arm of bell-crank |05 and is at all times in mesh with a gear |106 attached 3o the slide-wire support 4. The pinion |01 is adapted to alsobe meshed with either one of gears |08 or |09 that are constantly rotated by gear H0, which is driven from some source of power such as motor 25 that drives cam shaft 1|.

In the operation of this modication, as in that of Fig. 4, if the pointer |3 is in its midposition, neither ofthe edges 16a of actuating member 16 will engage an edge 85 as that member is moved upwardly by bell-crank 14. If, however, the pointer has deiiected to one side or the other, one of the edges 16a will engage one of the edges 86 on its upward movement and thereby tilt member 85. As this occurs, the pin |03 acting' in slot |04 will move bell-crank |05 suiciently to bring pinion |01 into mesh with one of the gears |08 or |09, and thereby rotate the slide-wire in the properl direction, depending .upon the deflection of the galvanometer pointer From the above-detailed description of the various modifications of our invention, it will be seen that we have provided a means for accurately adjusting a potentiometer slide-wire in ac-v cordance with the deviation of a galvanometer po'inter. The adjustment is according to time rather than according to distance, since adjustment is taking place during a certain length of time in each cycle rather than during the movement of a member. vBy this wemean that for a given deviation of the galvanometer pointer, the slide-wire or slide-wire contact will be`rotated a given amount of time from one of the constantly rotating members. This is an important feature since the amountof movement of the slide-wire contact during a predetermined time can be regulated to properly control some condition or process at a specified proper rate.

While in accordance with the provisions of the statutes, we have illustrated and described the best form of our invention now known to us, it will be apparent -to those` skilled in the art that changes may be made in the form of theapparatus disclosed without departing from the spirit of our invention as set forth in ,the appended claims, and that certain features ofour invention may sometimes be used to advantage without a corresponding use of other features.

We claim: 1. In a measuring instrument, a pointer deflected in accordance with a variable condition, means .for vclamping said pointer in'position, a

feeler adapted to move intoy contact with said.

pointer, a movable member positioned-in accordance with the-position of said feeler, means for moving said lmember, two oppositely'f rotating drive members, a mechanism adapted to be ad- "justed by said drive members, and means con- A trolled bythe movement ofsaid member "for efed to contact said pointer while it is clamped, a

member movable in accordance with the position of said feeler, an adjustable mechanism, means for adjusting said mechanism for a time dependent upon the position of the pointer, Asaid means consisting of a pair of oppositely rotatable drive members, and means for driving the mechanism by one of said drive members, said means being actuated by movement of said member.

` 3. In a measuring. instrument, a pointer movable in accordance with a measurable condition, means for clamping said pointer in position, a feeler for contacting said pointer while clamped, a member positioned by said feeler, an adjustable mechanism, a diierential consisting of a normally stationary part in driving relation With the mechanism and a normally rotatable part, a brake for the normally rotatable part, and means controlled by the position of said ymember to brake the normally rotatable partand thereby through the diierential cause the normally staable in accordance with a measurable condition,

means for clamping said pointer in place, a feeler positioned in accordance with the position of said pointer, a member positioned by said feeler, an adjustable mechanism, a drive member therefor, a tiltable element controlling said drive member when it is tilted, means for moving said member into engagement with said element to tilt it and thereby make it control the drive member to adjust said mechanism.

5. In a measuring instrument, a pointer movable in accordance with a measurable condition, a feeler adapted to engage said pointer, a member positioned by said` feeler, two oppositely rotating gears, a pinion adapted to engage either one of said gears, a tiltable element upon which said pinion is mounted, a periodically operated means to move said member after it is positioned, means operated by movement of said member to tilt said element and mesh said pinion with one of said gears, and an adjustable mechanism operated by said pinion.

6. In a measuring instrument, a pointer movable in accordance with a measurable condition, a feeler adapted to engage said pointer, a member positioned by said feeler, two oppositely rotating gears, a pinion adapted to engage either one of said gears; a tiltable element upon which said pinion is' mounted, a cam for moving said member into and out of engagement with said element, the part of said member engaging said element tilting the element and thereby moving the pinion into engagement with one of said gears, an adjustable mechanism, and means operated by said pinion to adjust said mechanism in accordance with the direction of its rotation.

'1. In a measuring instrument, a pointer movable to either side of a neutralposition in accordance with a measurable condition, a feeler for contacting said pointer, a member positioned on either side .of a neutral position by said .feeler in accordance'with the position o'f the pointer, two oppositely rotatable gears, a pinion adapted to mesh with either gear and4 mounted upon a one way, another part of said member engaging said element if the member is on the vother side ofl neutral to tilt the element the other way toV thereby cause the pinion to mesh with one or the other of said gears, and an adjustable mechanism driven by said pinion in accordance with its direction of rotation.

8. In a measuring instrument, a. pointer movable on either side of a neutral position in accordance 4with a measurable condition, a feeler contacting with said pointer, a member positioned in accordance with the position of said feeler and pointer, two oppositely rotating differentials each consisting of a pair of alternately moving parts, one of which is normally rotating and the other of which is normally stationary, means actuated in accordance withV the position of said member to Vbrake one of said normally rotating parts, an adjustable mechanism, and means to adjust said `mechanism from the normally stationary part which rotates when its corresponding rotating part is braked.

9. In a measuring instrument, a rotatable mechanism, a gear for rotating the mechanism, means for rotating said gear consisting of oppositely rotating drive members, a pointer movable in accordance with a measurable condition, a member moved `to a position corresponding to the position of the pointer, means for causing one of-sad drive membersto drive said gear, said means being controlled by said member. A

10. In a measuring instrument, a pair of oppositely rotating diierentials -each consisting of a normally rotating part and a. normally sta- `tionary part, an adjustable mechanism, means to change the setting'of the mechanism drivenby either of the normally stationary parts, a brake to act on either rotating part and thereby rotate the normally stationary part, through the differential to change the setting of the mechanism, a movable pointer, and means tomove the brake into engagement with one of the normally rotatable parts in accordance with the position of the pointer.

11. In a measuring-instrument, a-pointer deflectablein. accordance with a measurable condition, a feeler adapted to engage said pointer, a member moved by said feeler to a position cor-v responding to that of said pointer, means for thereafter moving said member through a predetermined path, an adjustable mechanism, a pair of oppositely rotating drive members for adjusting said mechanism, and means controlled by movement of said member through its path to adjust said mechanism by .one-of said drive members.

12. In a measuring instrument, a pointer movable in accordance with variations in a condition,

w a member, means to position said member to a position corresponding to -that of said pointer, a pair of oppositely rotating drive members, Aa mechanism adapted to be adjusted thereby,

, means to move said member after it is positioned to establish a driving connection between one' of said drive members and said mechanism.`

tioned, and means controlled thereby to cause one of said drive members to adjust said mechanism.v

14. In a measuring instrument, a pointer deected in accordance 'with a measurable condition, means for periodically clamping said pointer in position, a feeler adapted to contact said pointer while clamped, amovable member positioned by and inaccordance with said feeler, an adjustable mechanism, a pair of oppositely rotating drive members, means to move said .member after it is positioned, and means, controlled by the movement of said'mcmber to adjust said mechanism by one of said drive members.

15. -In a measuring instrument, a pointer deected in accordancewith variations in a measurable condition to either side of a neutral position, a pair of oppostely rotating diierentials, each consisting of a normally stationary part and a normally rotatable part, a support mechanically connected to each of the normally stationary parts, a member movable to a position corresponding to that of the pointer and brake means controlled by said member to stop one of said normally rotating parts to. thereby start rotation of the corresponding normally stationary part and drive the support.

16; In a measuring instrument, a pointer deflectable in accordance with a measurable condition, a feeler, means to move said feeler 'into contact with said pointer, a secondary feeler positioned by said feeler, means for applying a i brake to said secondary feeler and means to move said feeler away from said pointer, a member positioned by said secondary feeler'in accordance with the position of said pointer, a mechanism,

adjusting means therefor, and means movabler in accordance with the position of said member to permit an-adjustment of said mechanism by said adjusting means.

17.In a measuring instrument, a pointer deflectable in accordance with variations in a measurable condition, a feeler adapted to contact said pointer, a secondary feeler positioned by said feeler, a pair of cams adapted to engage said secondary feeler, a p air of oppositely rotating diierentials each consisting of a normally sta- .tionary part and a normally rotating part, a 

